A depth finder (also referred to as a fish finder) uses active sonar to detect fish and the bottom of a body of water. The depth finder then displays them on a graphical display device, such as an LCD or CRT screen. Depth finders generally operate by transmitting an electrical impulse to a transducer. The transducer converts the impulse into a sound wave, and directs the sound wave into the water. When the sound wave strikes the bottom, a fish, or some other object, it is reflected back to the transducer. The transducer senses the reflected sound wave, and transmits an electrical impulse back to the depth finder. The depth finder then measures the amount of time between when the electrical impulse was sent to the transducer and when the electrical impulse was received back from the transducer to determine the depth of the object that was struck by the sound wave. This process is repeated several times per second so that the depth finder is able to determine and display the bottom of the water, fish, and other objects.
One problem with present depth finders is that an accurate depth reading is not obtained when the transducer is rising and falling due to rough water. It is common for boats to operate in rough water (e.g., waves in excess of 2 feet). When waves on the water reach 2 feet, 3 feet, 4 feet, or even more, the boat rocks on the waves. With the transducer mounted on the boat, the transducer rises and falls as the boat rocks on the waves. When the transducer moves in this manner, the depth reading will rise and fall along with the transducer, which results in a bottom reading that is inaccurate and difficult to read.